1. Field of the Invention
The present invention relates to an optical image stabilizer, incorporated in optical equipment such as a camera or binoculars, for counteracting image shake due to vibrations such as hand shake.
2. Description of the Related Art
Image stabilizers (optical image stabilizers) for optical equipment prevent image shake from occurring on a focal plane by driving a part (image-stabilizing optical element) of an optical system relative to an optical axis thereof in accordance with the direction and the magnitude of vibration, such as hand shake, applied to the optical equipment. However, since the image-stabilizing optical element needs to be driven at high velocity in a fast responsive manner, such movement tends to be a burden on the driving mechanism therefor. Namely, the image-stabilizing optical element easily reaches a mechanical limit of movement thereof in the case where the magnitude of vibration is great, and the movement of the image-stabilizing optical element is easily restricted by some other reason. In such a movement limited state of the image-stabilizing optical element, further application of a driving force to the image-stabilizing optical element causes a driving force transfer mechanism for the image-stabilizing optical element to be subjected to mechanical stress and thus may cause damage to a low-strength portion of the driving force transfer mechanism. Additionally, in the case where the image-stabilizing optical element is supported by a support mechanism at all times to be freely movable, there is a possibility of the image-stabilizing optical element being moved forcibly if a strong external force is applied to the optical equipment in an accident, e.g., when the optical apparatus is accidentally dropped to the ground, which also causes the driving force transfer mechanism for the image-stabilizing optical element to be subjected to mechanical stress.
In the case of using a motor with a feed screw as a driving source for the image-stabilizing optical element, the less the lead angle (pitch) of the feed screw is, the more the accuracy of moving the image-stabilizing optical element (the mechanical resolution thereof) can be enhanced. However, a reduction of the lead angle of the feed screw is disadvantageous to the strength of the feed screw mechanism. Due to this fact, when a high-precision feed screw is adopted, the lead angle thereof being small, there is a possibility of the feed screw being damaged (e.g., the thread jamming). To prevent this problem from occurring, the range of movement of the image-stabilizing optical element can be increased so that the image-stabilizing optical element does not reach a mechanical limit of movement thereof easily, and the image-stabilizing optical element can be mechanically locked when not in operation. However, if the range of movement of the image-stabilizing optical element is increased, the image stabilizer may increase in size. If the image-stabilizing optical element is mechanically locked when not in operation, providing the image-stabilizing optical element with an independent locking mechanism for the image-stabilizing optical element may complicate the structure of the image stabilizer.